The use of substrates, such as those comprised of sapphire, Si, SiC, and ZnO in the fabrication of light emitting diodes (LEDs) is well known. Substrates are generally provided in the form of wafers. A single wafer can define substrates for many, e.g., hundreds or thousands, of LEDs. Layer of materials, such as semiconductors, conductors, and non-conductors, are formed upon such wafers to define the LEDs.
A problem encountered in the contemporary fabrication of LEDs is the undesirable build up of stress in the wafers or substrates, as well as in materials formed upon the wafer or substrate. Such stress can result in deformation, cracking, bending and/or bowing of the wafer or substrate. A deformed, cracked, bent and/or bowed wafer or substrate can result in the rejection of an entire wafer. There is presently a trend toward the use of larger wafers. Such stress related problems occur more frequently as the size of wafers increases and/or the coefficient of thermal expansion mismatch increases.
For example, stress can build up when a substrate having a layer of another material formed thereon is heated or cooled. The substrate and the layer can have substantially different thermal coefficients of expansion. This results in different rates of contraction and expansion between the substrate and the layer, thus causing stress.